1. Field of the Invention
The present invention relates to a lubrication structure of an engine that is suitable for a motorcycle, particularly a motorcycle that is used for off-road driving sports.
2. Background of the Invention
As an agitation loss is caused due to a crankshaft and other things when a motorcycle is run in a state in which lubricating oil accumulates in a crankcase of an engine, a reed valve is provided between a crank chamber and an oil pan to prevent the lubricating oil exhausted into the oil pan from the crank chamber from flowing in a reverse direction into the crank chamber. The reed valve is arranged vertically, that is, so that a valve element is open in a lateral direction of the body (see JP-A No. 2005-61387, for example).
However, the lubricating oil exhausted from the crank chamber flows laterally when the reed valve is vertically arranged and the valve element is formed so that it is open in the lateral direction of the body. Therefore, the lubricating oil is apt to stay in a space before and after the reed valve and an efficiency problem occurs, wherein the lubricating oil is not exhausted from the crank chamber sufficiently. On the other hand, a larger space is required for the lubricating oil exhausted from the reed valve on the downstream side of the engine when the reed valve is arranged horizontally so that the valve element of the reed valve is open downward. Therefore, the entire height of the engine is increased as a result and a problem occurs in that it is hard to secure a minimum road clearance (a distance from the ground to the lowest end of the engine).